What Are Gatsby Functions?
Gatsby Functions are serverless functions that run within your Gatsby project, deployed alongside your static site. They enable dynamic functionality typically associated with backend servers while maintaining the performance benefits of a static site architecture. This approach eliminates the need for separate backend infrastructure, reducing complexity and deployment overhead.
The key advantage lies in the unified development experience. Front-end developers can extend their capabilities without learning entirely new frameworks or languages. Your API code lives in the same repository as your front-end code, shares dependencies, and deploys through the same pipeline. This integration streamlines development and maintenance while providing powerful serverless capabilities.
Gatsby Functions handle a wide range of use cases including form submissions, user authentication, secure API integrations with external services, building REST or GraphQL APIs, and processing data on demand. The automatic scaling and pay-per-invocation model means you only pay for what you use, making it cost-effective for projects of any size.
Explore our approach to modern web development and see how serverless technologies can transform your projects.
Build complete backend functionality without managing servers
Form Submissions
Process form data directly without third-party services
User Authentication
Implement login, registration, and session management
External API Integration
Securely connect to third-party services with protected credentials
REST APIs
Build complete RESTful APIs using familiar conventions
Data Processing
Transform and process data on demand
Webhooks
Receive and handle webhooks from external services
Setting Up Your First API Endpoint
Creating a Gatsby Function follows a simple file-based convention. Place your function files in the src/api directory of your Gatsby project, and Gatsby automatically routes them to URL endpoints. The filename determines your API path, so src/api/hello.js becomes accessible at /api/hello.
Each function exports a default handler that receives request and response objects, following the familiar Express.js pattern. The handler receives a standard HTTP request with methods, headers, and body data, and returns responses using familiar status codes and JSON formatting. This familiar API makes the transition seamless for developers experienced with Node.js backends.
The function structure remains consistent regardless of complexity. Simple endpoints return immediate responses, while more complex functions can read request bodies, query parameters, and headers to build dynamic responses. This flexibility allows you to scale from simple data returns to complex processing workflows within the same framework.
Learn more about our development process for building modern web applications.
1// src/api/hello.js2export default function handler(req, res) {3 res.status(200).json({ message: "Hello from Gatsby Functions!" });4}Understanding HTTP Methods
Gatsby Functions support standard HTTP methods, enabling you to build RESTful APIs that follow established conventions. The method determines how your function processes requests and what actions it performs. Proper method handling ensures your API behaves predictably and integrates well with front-end applications and external services.
GET requests retrieve data without modifying server state. Your handlers can read query parameters from the request URL and return appropriate data based on those parameters. This approach suits data fetching, search functionality, and any operation that simply retrieves information.
POST requests send data to be processed, typically creating new resources or triggering actions. Your handler receives the request body, which Gatsby parses automatically for form submissions and JSON payloads. This method suits form submissions, user registrations, and any operation that creates or modifies data.
PUT and PATCH requests update existing resources, with PUT replacing entire resources and PATCH modifying specific fields. DELETE requests remove resources. Supporting these methods requires examining req.method in your handler and routing accordingly, enabling full CRUD (Create, Read, Update, Delete) functionality.
When building RESTful APIs, consider how these endpoints integrate with your overall architecture for seamless data flow across your application.
1export default function handler(req, res) {2 switch (req.method) {3 case 'GET':4 // Retrieve and return data5 res.status(200).json({ data: getData() });6 break;7 case 'POST':8 // Create new data from request body9 const newData = createData(req.body);10 res.status(201).json({ success: true, data: newData });11 break;12 case 'PUT':13 // Update existing data14 updateData(req.body);15 res.status(200).json({ success: true });16 break;17 case 'DELETE':18 // Remove data19 deleteData(req.query.id);20 res.status(204).send();21 break;22 default:23 res.status(405).json({ error: 'Method not allowed' });24 }25}Handling CORS and Headers
Cross-Origin Resource Sharing (CORS) becomes essential when your API needs to serve requests from different domains. Without proper CORS configuration, browsers block cross-origin requests for security reasons. Gatsby Functions make CORS handling straightforward through response headers.
Setting the Access-Control-Allow-Origin header enables requests from specified origins. For development or public APIs, you might allow all origins with '*'. Production applications typically restrict this to specific trusted domains, maintaining security while enabling necessary cross-origin access.
Beyond CORS, you can set custom headers for authentication tokens, content types, caching directives, and any other HTTP header requirements. This flexibility enables integration with various authentication schemes, content negotiation, and API versioning strategies.
Proper CORS configuration is critical when building integrated solutions that connect multiple services or domains together.
1export default function handler(req, res) {2 // Enable CORS for all origins3 res.setHeader('Access-Control-Allow-Origin', '*');4 5 // Handle preflight OPTIONS requests6 if (req.method === 'OPTIONS') {7 res.setHeader('Access-Control-Allow-Methods', 'GET, POST, PUT, DELETE');8 res.setHeader('Access-Control-Allow-Headers', 'Content-Type, Authorization');9 return res.status(204).send();10 }11 12 // Process request13 res.status(200).json({ message: "CORS configured" });14}Working with Environment Variables
Environment variables provide secure storage for sensitive configuration like API keys, database credentials, and service endpoints. Gatsby Functions access these variables through process.env, ensuring secrets remain separate from your codebase and are only exposed in deployment environments.
Development variables live in .env.development files, while production values come from your hosting provider's environment configuration. This separation prevents accidental exposure of production secrets during development and ensures deployment-specific values are applied automatically.
When deploying to Gatsby Cloud or Netlify, configure environment variables through their respective dashboards. These platforms encrypt stored values and inject them into your function's environment automatically. This approach keeps secrets secure while making them available where needed.
Security is paramount when handling sensitive data - proper environment variable management protects your credentials while enabling dynamic functionality.
1export default async function handler(req, res) {2 const apiKey = process.env.EXTERNAL_API_KEY;3 4 if (!apiKey) {5 return res.status(500).json({ error: 'API key not configured' });6 }7 8 const response = await fetch('https://api.example.com/data', {9 headers: {10 'Authorization': `Bearer ${apiKey}`,11 'Content-Type': 'application/json'12 }13 });14 15 const data = await response.json();16 res.status(200).json(data);17}Common Use Cases
Form Submissions
Form submissions represent one of the most common Gatsby Functions use cases. Rather than relying on third-party form services, you can process submissions directly within your project. This approach provides complete control over data handling, validation, and storage integration.
User Authentication
Implement login, registration, and session management. While you typically combine this with a dedicated auth service like Auth0 or Firebase, Gatsby Functions handle token verification, protected route enforcement, and custom claim processing. This integration creates seamless authentication experiences within your static site.
External API Integration
External API integration benefits from serverless function architecture because it keeps API keys server-side. Direct calls from browser JavaScript would expose keys, but Gatsby Functions proxy these requests securely. Your function authenticates with external services and returns processed data to your front end, maintaining security while enabling rich integrations.
Dynamic Content Generation
Generate personalized content on demand, including customized reports, processed files, or dynamic pages based on user input. The serverless approach handles these tasks without requiring an always-running server, scaling automatically with demand.
These capabilities power modern digital experiences while maintaining the performance benefits of static site architecture.
Deployment and Production Considerations
Deploying Gatsby Functions follows the same process as deploying your Gatsby site. When you push code to your git repository, your hosting provider builds both your static content and your API functions automatically. This unified deployment simplifies operations and ensures consistency between your front end and API.
Gatsby Cloud provides native support for Gatsby Functions, automatically recognizing and deploying API endpoints. The platform handles scaling, monitoring, and logging without additional configuration. Alternative platforms like Netlify and Vercel also support Gatsby Functions, each offering unique features and deployment workflows.
Production Best Practices
- Monitor function performance and review logs regularly to identify issues early
- Set up alerts for error rates and track invocation counts to understand usage patterns
- Implement health checks for infrequently called functions to avoid cold start latency
- Test in staging environments before production deployment to catch environment-specific issues
Monitoring function performance and errors requires attention in production environments. Cold starts can introduce latency for infrequently called functions, so consider implementing warming functions for critical applications where response time is crucial.
Best Practices for API Development
Structure your API files thoughtfully as your project grows. Group related endpoints into directories, creating logical organization that mirrors your API's resource structure. A RESTful design might organize endpoints like src/api/users/profile.js for user profile operations, maintaining clarity as your API expands.
Implement proper error handling throughout your functions. Return meaningful error messages with appropriate HTTP status codes, helping front-end applications respond appropriately to failure conditions. Avoid exposing internal error details that could reveal implementation specifics to potential attackers.
Validate all input before processing. User-submitted data requires thorough validation to prevent security vulnerabilities and ensure data integrity. Use validation libraries or implement custom checks appropriate to your data types and business requirements.
Document your API endpoints with clear comments and consider generating OpenAPI specifications for more complex APIs. This documentation helps team members understand available endpoints and their expected inputs and outputs, accelerating development and maintenance.
Test your functions thoroughly, including edge cases and error conditions. While Gatsby Functions run in a Node.js environment, differences between local development and production environments can cause unexpected issues. Test deployment configurations, environment variable handling, and external service integration in staging environments before production deployment.
Following these best practices ensures robust, maintainable APIs that scale with your business needs.
Frequently Asked Questions
What hosting platforms support Gatsby Functions?
Gatsby Cloud provides native support, and Netlify and Vercel also support Gatsby Functions with their respective serverless function offerings.
How do Gatsby Functions handle scaling?
Gatsby Functions scale automatically based on demand. The serverless model handles traffic spikes without manual intervention.
Can I use Gatsby Functions for database operations?
Yes, Gatsby Functions can connect to databases using environment variables for credentials, enabling CRUD operations within your API.
What are the limits on request/response size?
Limits vary by hosting provider. Generally, request bodies should remain under 4-5MB for optimal performance.